Process of manufacturing concentrated nitric acid.



Patented Jan. 14, 1913.

M. MOEST, R. M. VON BERNEOK 6; J. OPLL PROCESS OF MANUFACTURINGGONGENTRATED NITRIC ACID. APPLICATION FILED JULY 26, 1911. 1,050,100.

U ITED sTA Es PATENT OFFICE,

MARTIN MOEST AND RUDOLF M'ULLER VON BERNECK, or HocHsT-oN-THE-MAIN, AND'JOSEF OPL, or LoRsBncH, GERMANY, ASSIGNORS T0 FARBWERKE voRM. MEIsTERLUCIUS & BRfiNING, or HocHsT-oN-THE-MAIN, GERMANY, A CORPORATION OF GANY.

PROCESS OF MANUFACTURING CONCENTRATED NITRIC ACID.

To all whom it may concern: I

Be it known that we, MARTIN MOEST, Ph, D., RonoLr MI'jLLER voN BERNECK,and JosEF OPL, chemists, citizens of the Empires of Germany andAustria-Hungary, respectively, the first two'residing atHochst-onthe-Main, Germany, and the third at Lorsbach a. T., Germany,have invented certain new and useful Improvements in Nitric Acid of HighPercentage and Processes of Making Same, of which the following is aspecification.

By the method, hitherto in use in the manufacture of nitric acid,consisting in causing NO gases to act upon water in presence of oxygen,only a comparatively diluted nitric acid is obtained. Thus with mixturesof nitric oxid and air an acid of only -52 per cent. strength isproduced. With regard to mixtures of pure nitrogen peroxid gas withoxygen, Foerster and Koch (see Zez'tsohm'ft fair ange'wandte Ohemie,1908, page .2168) have shown that the highest concentration of nitricacid obtainable is an acid of about 68 per cent. strength, namely theacid of the lowest vapor-pressure. From their experiments and fromtheoretical considerations the said authors draw the followingconclusion There is no doubt that the highest concentration of nitricacid obtainable by the action of nitrogen peroxid and excess of oxygenupon water at ordinary temperature, scarcely exceeds 69 per cent. Inpractice it was not possible to obtain in this manner an acid of agreater strength than 60-62 per cent. This fact is unfortunate,particularly because for industrial purposes there is principallyrequired an acid of 70-80 per cent. strength for the preparation of themixed acid mostly used for nitrating purposes, Whereas nitric acid of apercentage strength below 70 is employed only to a comparatively smallextent.

esses for the concentration of' the dilute nitric acid obtained fromoxids ofqnitrogen Specification of Letters Patent.

Application filed July 26, 1911.

p In consequence of this therev have been elaborated of late numerousproc Serial No. 640,647.

by their action upon water in presence of Patented Jan. 14, 1913.

excess of oxygen. These processes are however for the most partcomplicated andin any case expensive.

Now contrary to the technical and theoretical considerations hithertoentertained, we have found a process for manufacturing directly fromnitrogen peroxid (or nitrogen tetroxid), water and oxygen at ordinaryatmospheric pressure, a nitric acid containing 7 0 per cent. and more ofI-INO This process, which constitutes our present invention,-

consists in enriching nitric acid obtained in the usual manner, forinstance acid of 6062 per cent. strength, with nitrogen peroxid, whicheasily dissolves in the acid, and in then subjecting this nitric acidcontaining nitrogen peroxid, ina finely subdivided state to the actionof oxygen. In consequence of the increased concentration of the N 0 thespeed of the reaction is increased in the sense of the equation 2NO +H OHNO-l-HNO while at the same time the evaporation of I-INO which isantagonistic to the concentration, is checked by avoiding a considerableexcess of oxyg en. The non-oxidized part of the nitrogen peroxid or ofthe nitrous acid, that maybe present in solution, is expelled by theoxygen introduced at the end of the reaction system, so that the nitricacid finally obtained is practically free from nitrous acid.

For carrying out our new process it is advantageous to use a systemadapted to fulfil the following conditions :The first part of the systemproduces a nitric acid of simultaneously, if required, introducingoxygen; in the third part of the system oxygen is introduced for thepurpose of converting nitrogen peroxid into nitric acid and expellingthe unused oxids of nitrogen. In practice it is advantageous to work onthe counter-current principle and continuously in such a manner that atone end of the system water is introduced and at the other end theconcentrated nitric acid is drawn oli' whereas the oxygen and thenitrogen peroxid gases pass in the opposite direction. The several partsof the system may consist of the known trickling-towers or of a systemof vessels in which, either by means of spraying nozzles, agitators orany other suitable device, the nitric acid containing N0 is brought intointimate contact with the oxygen. The nitrogen peroxid or nitrogentetroxid may be introduced at suitable points either inliquid orvaporous form or mixed with oxygen. It has been found particularlyadvantageous to introduce the nitrogen peroxid in such a manner that thecurrent of oxygen is passed through liquid nitrogen peroxid wherebyexactly regulated quantities of the nitrogen peroxid can be introducedinto the reaction system by operating at determined temperatures. Theoxygen is introduced either exclusively at the end of the system or atseveral points as required. When starting from nearly pure oxygen andnearly pure nitrogen peroxid in proper proportions, it is possible, asboth gases are consumed, to carry on the process in such a manner thatat the end of the system only very small quantities of gas escape sothat losses owing to entrainment of nitric acid vapors are entirelyavoided. In practice, however, it is advantageous to work with a smallexcess of oxygen which,

a in order to avoid losses of oxygen is reintroduced into the process bysuitable devices. It is not necessary to charge the whole system withpure oxygen, but there may be prepared nitric acid of a lowerconcentration in the usual manner from N0 water and air, and the dilutenitric acid thus obtained may be further treated, as above indicated,with NO and oxygen; thus a considerable saving of oxygen is effected. Ofcourse it is possible to combine these arrangements.

The accompanying drawing illustrates suitable apparatus for carrying outthe process, the figure being a side elevation. The absorption chambersT T T and T in which the nitrogen-oxids are converted into nitric acidwith the aid-of oxygen and water, are connected with each other bygaspipes G. In chamber T the non-oxidized nitric oxid gases from thenitric acid are expelled, with the aid of oxygen. The introduction ofthe water and the dilute nitric acid is eifected at H O; that of thenitricoxids-alone or mixed with oxygenat rea ies N0 and of the oxygen at0. These gas-es flow through the system in the direction'indicated bythe arrows beside pipes Gr, while the water and the dilute nitric acidpass through the apparatus in the reverse direction, from the bottom ofone chamber, through the lifting device, to the top of the next chamber.D D and D are devices for lifting the nitric acid loaded with nitricgases. The finished product is discharged from chamber T at B. In thereaction which takes place, two molecules of NO require one molecule ofwater and half a molecule of oxygen. Gonsequently, there are requiredfor the oxidation of 92 grams of N0 into nitric acid 12 liters ofoxygen. In practice, a small excess of oxygen is employed so that nonitrogen oxids escape from the apparatus, but only oxygen. Theinitialtemperature is that of the surrounding air, and as the reaction isattended by evolution of heat, a rise of the tempreature gradually setsin which depends on the radiation and on the quantity of the nitric-oxidused, per time-unit. We have found that the best reaction takes place if5-l0 kg. of nitrogen peroxid per cubic meter of the reaction area andper hour are employed, according to the desired concentration of theacid. If it is intended to prepare a strong acid, less of the nitrogenperoxid should be used than if an acid of a lower strength is desired.

Having now described our invention what we claim is: 1

1. The process of manufacturing, in a direct way, highly concentratednitric acid, which consists in enriching the dilute nitric acid,obtained in the usual manner, with nitrogen peroxid and treating thismixture with oxygen.

2. The process of manufacturing, in a direct way, highly concentratednitrlc acid, 105 which consists in enriching the dilute nitric acid,obtained in the usual manner, with nitrogen peroxid in a gaseous form,and treating this mixture with oxygen.

3. The process of manufacturing, in a di- 110 rect way, highlyconcentrated nitric acid, which consists in enriching the dilute nitricacid, obtained in the usual manner, with nitrogen peroxid which isintroduced into the nitric acid in a vaporous form with the aid 115 of acurrent of oxygen, and treating this mixture with oxygen.

4. The process of manufacturing, in a direct way, highly concentratednitric acid,

which consists in enriching the dilute nitric 5. The process ofmanufacturing, in a di- In testimony whereof, we aflix our signa- 10rect way, highly concentrated nitric acid, tures in presence of twowitnesses. which consists in treating dilute nitric acid,

obtained in the usual manner, with a mix- MARTIN-MQEST' ture of nitrogenperoxid and oxygen and g ggfigfi VON BERNEGK" further treating thismixture With oxygen,

introduced at the end of the reaction-appa- Witnesses:

ratus, thereby expelling the non-oxidized JEAN GRUND,

nitric oxid gases from the nitric acid. CARL GRUND.

